The present invention generally relates to liquid-cooled heat sinks, and more particularly to a liquid-cooled heat sink for electronic devices that includes obstructions for optimizing turbulence and increasing surface area for effective heat transfer to the stream of liquid.
The performance of electronic circuits and their semiconductor devices is limited by temperature. Semiconductor device performance degrades when the internal temperature reaches or exceeds a particular limit. That limit depends upon the nature of the semiconductor device. In order to maintain or increase the performance of such devices, they must be cooled in some way. The manner of cooling depends upon many parameters, including the space available for the cooling process, the temperatures to be encountered, power, etc. In some instances simply passing a fluid over the device or, over a finned heat sink that is attached to the device, is sufficient to maintain the semiconductor at safe operating temperatures.
In one known semiconductor device cooling technique, convecting fins are attached to a semiconductor package, or the package is affixed to a larger metal member, referred to as a heat sink or cold plate. This heat sink draws heat away from the semiconductor device and can be air cooled or liquid cooled, depending upon the particular application. If the heat sink is air cooled it will typically have heat convecting fins.
Different cooling fluids may be used, when liquid cooled methods are employed, depending upon the application and the density of the electronic devices in a given circuit. Boiling liquids are often used, such as fluorinated hydrocarbon refrigerants, which are delivered to the cold plate in liquid form and are boiled to remove heat. These systems often have the highest heat removal rate for a limited xe2x80x9ccold platexe2x80x9d area, but require a considerable amount of power to operate, i.e. to be pumped to and from the heat transfer site. In other systems, a cold liquid is circulated through the cold plate with the cold liquid being refrigerator cooled, evaporatively cooled, or convectively cooled.
A problem exists in the foregoing prior art systems in that a portion of the liquid used to cool the semiconductor device tends to stagnate in a region close to the surface of the heat sink. This stagnation typically refers to a reduction in coolant speed near the heat sink surface. Here the coolant flows at a slower than required speed to adequately remove heat from the heat sink surface. This stagnation reduces the effectiveness of the heat transfer in the cooling system. Very often, the rate of cooling is less than the rate at which heat arrives at that interface surface, which causes an accumulation of heat at the surface. Several options have been proposed in the art to reduce this effect, including increasing the speed of the flow of the coolant or introducing structural features which cause turbulent flow and increased effective surface area.
For example, in U.S. Pat. No. 5,316,075, issued to Quon, a liquid-cooled heat sink is disclosed that includes a planar baffle with only one inlet plenum and one outlet plenum. Holes are formed within the baffle, in parallel rows, to produce jets of liquid coolant within the heat sink. In one embodiment, a mounting plate includes a forest of pins extending downward from its undersurface. The pins are inserted in holes in a mounting plate and extend toward the bottom surface of the mounting plate. The pins each have free ends, and are on centers half the distance of the centers of liquid injection/removal nozzles. There is no pin directly opposite a nozzle. When assembled, a space between the pins is directly opposite the nozzles so that the liquid jet issuing from the nozzle strikes the undersurface of a mounting plate. As the liquid leaves that strike area and travels to the outlet nozzle, it passes through the forest of pins. Quon""s pins must be rectangularly arranged on rectangular centers, and be half the distance between the nozzles.
A number of disadvantages exist with this approach. For one thing, a perforated baffle is used to produce jets of liquid in order obtain a very high flow rate of liquid to achieve adequate average flow and to reduce stagnation of the coolant. This flow requires a larger, more expensive pump, even though the back pressure across the baffle is low. For another thing, Quon""s pins must be rectangularly arranged on rectangular centers which is wholly inadequate to produce optimum turbulence in the flowing coolant. Quon also relies primarily upon his arrangement of plenums, baffles and jet producing holes to reduce or eliminate the stagnation region. This arrangement of parts is not only cumbersome to manufacture and assemble, but is wholly unnecessary to reduce or eliminate coolant stagnation at the region close to the surface of the heat sink.
A liquid-cooled heat sink is provided having a housing including a peripheral side wall extending from the perimeter of a bottom wall and a lid sized to engage the peripheral side wall so as to form a chamber. A fluid inlet port and a fluid outlet port are defined through the lid, and disposed in fluid communication with the chamber. A plurality of pins project outwardly from the bottom wall so as to be positioned within the chamber and arranged in a staggered pattern. The pins include an end that engages the lid to provide structural support, and to prevent deflection of the lid by high liquid pressure.
In one alternative embodiment of the invention, a liquid-cooled heat sink is provided having a housing including a peripheral side wall extending from the perimeter of a bottom wall and a lid sized to engage the peripheral side wall so as to form a chamber. A fluid inlet port and a fluid outlet port are defined through the lid, and disposed in fluid communication with the chamber. A fin having a plurality of corrugations is positioned within the chamber so that at least one of the corrugations engages the bottom wall and at least one of the corrugations engages the under surface of the lid.